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ABSTRACT: The purpose of this study was to assess as a potential means of limiting radiation exposure the effect on perfusion CT values of increasing sampling intervals in lung perfusion CT acquisition.
Lung perfusion CT datasets in patients with lung tumors (> 2.5 cm diameter) were analyzed by distributed parameter modeling to yield tumor blood flow, blood volume, mean transit time, and permeability values. Scans were obtained 2-7 days apart with a 16-MDCT scanner without intervening therapy. Linear mixed-model analyses were used to compare perfusion CT values for the reference standard sampling interval of 0.5 second with those of datasets obtained at sampling intervals of 1, 2, and 3 seconds, which included relative shifts to account for uncertainty in preenhancement set points. Scan-rescan reproducibility was assessed by between-visit coefficient of variation.
Twenty-four lung perfusion CT datasets in 12 patients were analyzed. With increasing sampling interval, mean and 95% CI blood flow and blood volume values were increasingly overestimated by up to 14% (95% CI, 11-18%) and 8% (95% CI, 5-11%) at the 3-second sampling interval, and mean transit time and permeability values were underestimated by up to 11% (95% CI, 9-13%) and 3% (95% CI, 1-6%) compared with the results in the standard sampling interval of 0.5 second. The differences were significant for blood flow, blood volume, and mean transit time for sampling intervals of 2 and 3 seconds (p ≤ 0.0002) but not for the 1-second sampling interval. The between-visit coefficient of variation increased with subsampling for blood flow (32.9-34.2%), blood volume (27.1-33.5%), and permeability (39.0-42.4%) compared with the values in the 0.5-second sampling interval (21.3%, 23.6%, and 32.2%).
Increasing sampling intervals beyond 1 second yields significantly different perfusion CT parameter values compared with the reference standard (up to 18% for 3 seconds of sampling). Scan-rescan reproducibility is also adversely affected.
American Journal of Roentgenology 02/2013; 200(2):W155-62. · 2.78 Impact Factor
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ABSTRACT: To assess the impact on absolute values and reproducibility of adding portal venous (PV) to arterial input functions in computed tomographic perfusion (CTp) evaluations of liver tumors and normal liver.
Institutional review board approval and written informed consent were obtained; the study complied with Health Insurance Portability and Accountability Act regulations. Computed tomographic perfusion source data sets, obtained from 7 patients (containing 9 liver tumors) on 2 occasions, 2 to 7 days apart, were analyzed by deconvolution modeling using dual ("Liver" protocol: PV and aorta) and single ("Body" protocol: aorta only) vascular inputs. Identical tumor, normal liver, aortic and, where applicable, PV regions of interest were used in corresponding analyses to generate tissue blood flow (BF), blood volume (BV), mean transit time (MTT), and permeability (PS) values. Test-retest variability was assessed by within-patient coefficients of variation.
For liver tumor and normal liver, median BF, BV, and PS were significantly higher for the Liver protocol than for the Body protocol: 171.3 to 177.8 vs 39.4 to 42.0 mL/min per 100 g, 17.2 to 18.7 vs 3.1 to 4.2 mL/100 g, and 65.1 to 78.9 vs 50.4 to 66.1 mL/min per 100 g, respectively (P < 0.01 for all). There were no differences in MTT between protocols. Within-patient coefficients of variation were lower for all parameters with the Liver protocol than with the Body protocol: BF, 7.5% to 11.2% vs 11.7% to 20.8%; BV, 10.1% to 14.4% vs 16.6% to 30.1%; MTT, 4.2% to 5.5% vs 10.4% to 12.9%; and PS, 7.3% to 12.1% vs 12.6% to 20.3%, respectively.
Utilization of dual vascular input CTp liver analyses has substantial impact on absolute CTp parameter values and test-retest variability. Incorporation of the PV inputs may yield more precise results; however, it imposes substantial practical constraints on acquiring the necessary data.
Journal of computer assisted tomography 07/2012; 36(4):388-93. · 1.38 Impact Factor
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ABSTRACT: To assess the reproducibility of computed tomographic (CT) perfusion measurements in liver tumors and normal liver and effects of motion and data acquisition time on parameters.
Institutional review board approval and written informed consent were obtained for this prospective study. The study complied with HIPAA regulations. Two CT perfusion scans were obtained 2-7 days apart in seven patients with liver tumors with two scanning phases (phase 1: 30-second breath-hold cine; phase 2: six intermittent free-breathing cines) spanning 135 seconds. Blood flow (BF), blood volume (BV), mean transit time (MTT), and permeability-surface area product (PS) for tumors and normal liver were calculated from phase 1 with and without rigid registration and, for combined phases 1 and 2, with manually and rigid-registered phase 2 images, by using deconvolution modeling. Variability was assessed with within-patient coefficients of variation (CVs) and Bland-Altman analyses.
For tumors, BF, BV, MTT, and PS values and reproducibility varied by analytical method, the former by up to 11%, 23%, 21%, and 138%, respectively. Median PS values doubled with the addition of phase 2 data to phase 1 data. The best overall reproducibility was obtained with rigidly registered phase 1 and phase 2 images, with within-patient CVs for BF, BV, MTT, and PS of 11.2%, 14.4%, 5.5% and 12.1%, respectively. Normal liver evaluations were similar, except with marginally lower variability.
Absolute values and reproducibility of CT perfusion parameters were markedly influenced by motion and data acquisition time. PS, in particular, probably requires data acquisition beyond a single breath hold, for which motion-correction techniques are likely necessary.
Radiology 09/2011; 260(3):762-70. · 5.73 Impact Factor
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ABSTRACT: The purpose of this article is to assess the variability of perfusion CT measurements in lung tumors and the effects of motion and duration of data acquisition on perfusion CT parameter values.
Two perfusion CT scans were obtained in 11 patients with lung tumors, 2-7 days apart, using phase 1 scans (30-second breath-hold cine) followed by phase 2 scans (six intermittent helical breath-holds), spanning 125 seconds. Tumor blood flow (BF), blood volume (BV), mean transit time (MTT), and permeability were calculated for phase 1 using all-cine and motion-corrected (rigidly registered) images, both with and without matching phase 2 images (manually or rigidly registered). Variability was assessed by the within-patient coefficient of variation (CV) and Bland-Altman analyses.
BF, BV, MTT, and permeability values varied widely by method of analysis (median BF, 45.3-65.1 mL/min/100 g; median BV, 2.6-3.8 mL/100 g; median MTT, 3.6-4.1 seconds, and median permeability, 13.7-39.3 mL/min/100 g), as did within-patient CVs (10.9-114.4%, 25.3-117.6%, 22.3-51.5%, and 29.6-134.9%, respectively). Parameter values and variability were affected by motion and duration of data analyzed: permeability values doubled when phase 2 images were added to phase 1 data. Overall, the best reproducibility was obtained with registered phase 1 and 2 data, with within-patient CVs of 11.6%, 26.5%, 45.4%, and 30.2%, respectively.
The absolute values and reproducibility of perfusion parameters in lung tumors are markedly influenced by motion and duration of data acquisition. Permeability, in particular, probably requires data acquisition beyond a single breath-hold. The smallest variability in parameter values was obtained with motion correction and extended acquisition durations.
American Journal of Roentgenology 07/2011; 197(1):113-21. · 2.78 Impact Factor
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ABSTRACT: The purpose of this article is to assess tumor changes on perfusion CT with bevacizumab and interferon (IFN) therapy in patients with metastatic carcinoid tumors and to evaluate perfusion CT differences between the two therapies.
In a phase 2 clinical trial, 44 patients were randomized to receive monotherapy with bevacizumab or IFN for 18 weeks (stage 1), followed by dual-therapy with both drugs (stage 2). Twenty-four patients consented to have optional perfusion CT examinations, which were undertaken at baseline and 18 weeks and at intervening 2 days (bevacizumab arm) or 9 weeks (IFN arm), and subsequently at 2 days after the addition of bevacizumab (IFN arm) and 9 weeks after the addition of IFN (bevacizumab arm). Tumor blood flow, blood volume, and permeability were evaluated.
In the bevacizumab arm (n = 12), mean (± SD) blood flow reduced significantly after 2 days compared with baseline (16.2 ± 6.9 vs 32.3 ± 21.3 mL/min/100 g; p = 0.02), a 41.4% reduction (p < 0.0001) that was relatively fixed. Blood volume was similarly reduced from baseline values (2.8 ± 1.3 vs 4.3 ± 2.1 mL/100 g; p = 0.02), a 27.9% reduction (p < 0.02). Both measures remained essentially unchanged at 18 weeks. Similar changes in blood flow and blood volume were observed with the addition of bevacizumab in stage 2. No significant changes in blood flow or blood volume were detected in the IFN arm (n = 12), and no significant changes in permeability were detected in either arm.
Perfusion CT detects significant changes in perfusion parameters in metastatic carcinoid tumors treated with bevacizumab. Such changes are apparent just 2 days into therapy, are sustained, and are significantly different from those associated with IFN treatment. Tumor blood flow decreased with bevacizumab treatment by a relatively fixed percentage relative to baseline measurements.
American Journal of Roentgenology 03/2011; 196(3):569-76. · 2.78 Impact Factor
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ABSTRACT: To compare the relative performance of one-dimensional (1D) manual, rigid-translational, and nonrigid registration techniques to correct misalignment of lung tumor anatomy acquired from computed tomography perfusion (CTp) datasets.
Twenty-five datasets in patients with lung tumors who had undergone a CTp protocol were evaluated. Each dataset consisted of one reference CT image from an initial cine slab and six subsequent breathhold helical volumes (16-row multi-detector CT), acquired during intravenous contrast administration. Each helical volume was registered to the reference image using two semiautomated intensity-based registration methods (rigid-translational and nonrigid), and 1D manual registration (the only registration method available in the relevant application software). The performance of each technique to align tumor regions was assessed quantitatively (percent overlap and distance of center of mass), and by a visual validation study (using a 5-point scale). The registration methods were statistically compared using linear mixed and ordinal probit regression models.
Quantitatively, tumor alignment with the nonrigid method compared to rigid-translation was borderline significant, which in turn was significantly better than the 1D manual method: average (± SD) percent overlap, 91.8 ± 2.3%, 87.7 ± 5.5%, and 77.6 ± 5.9%, respectively; and average (± SD) DCOM, 0.41 ± 0.16 mm, 1.08 ± 1.13 mm, and 2.99 ± 2.93 mm, respectively (all P < .0001). Visual validation confirmed these findings.
Semiautomated registration methods achieved superior alignment of lung tumors compared to the 1D manual method. This will hopefully translate into more reliable CTp analyses.
Academic radiology 03/2011; 18(3):286-93. · 2.09 Impact Factor
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ABSTRACT: To compare blood flow measurements of tumors assessed by perfusion computed tomography (pCT) and the clinical gold standard of 15O-labeled water positron emission tomography (15O-PET).
Blood flows were estimated by pCT (4-row multidetector, CT Perfusion 3.1) and 15O-PET (Posicam, first-pass model) in 14 patients with solid tumors, totaling 22 index tumors and 57 matched pairs of examinations. Blood flow estimates were compared using t test, Bland-Altman, and linear mixed regression analyses.
There was no significant difference between the mean (SD) blood flow values measured by pCT and 15O-PET: 25.9 +/- 15.4 and 27.8 +/- 14.0 mL/min per 100 g, respectively.
The demonstration of a good correlation between pCT and 15O-PET potentially enables the use of pCT, which is more widely available than 15O-PET, when tumor blood flow estimates are required, particularly in the context of clinical studies.
Journal of computer assisted tomography 33(3):460-5. · 1.38 Impact Factor
